Goldman Sachs ended 2010 on a "financially humbling note," with its fourth-quarter profits down 52 percent from the same period in 2009. This was the third straight decline in quarterly profits at the Wall Street giant, and investors are worried that what seemed like a passing trend may signal a serious issue. (Watch a New York Times report looking inside Goldman Sachs.) What's behind Goldman Sachs' continuing slide in profits? Here, three factors:

1. Investors got spooked
Fourth-quarter revenue from Goldman's "usual engine for growth" — its bond, currency, and commodities business — was half what it was a year ago, says David Reilly in The Wall Street Journal. That decline reflected both a "seasonal slowdown in trading" and a growing wariness among skittish investors as interest rates changed abruptly. That's not good news for a line of business that helped Goldman post record profits in 2009.

2. Staff costs are too high
Even as revenue slowed, Goldman "bulked up in 2010," says Colin Barr in Fortune. In a bid to snap up talent, the bank expanded its full-time staff by nine percent. As a result, even though the average pay per worker fell by 14 percent from its 2009 levels, compensation and benefits still sucked up almost 40 percent of the firm's net revenue. Perhaps Goldman has "gotten too fat to succeed."

3. A lack of diversity
Unlike most of its rivals, Goldman Sachs does not have a retail arm, says Daniel Indiviglio at The Atlantic. So while JP Morgan and Wells Fargo were able to counter the slowdown on Wall Street with revenue from Main Street, Goldman was not. The bank's "concentration in investment banking and trading" hurt it in 2010, and, moving forward, the "additional financial regulation" in those markets will only exacerbate the situation.